This invention relates to the recovery of crude oils from subterranean formations, and more particularly to the recovery of such crude oils which are highly acidic in character. The invention is especially directed to the recovery of such acidic crude oils which are highly viscous. By "highly viscous" is meant those crudes having a viscosity of at least on the order of about 1000 cp at 75.degree. F. Although the invention finds its primary utility in connection with the more viscous crudes, it may also be used in some contexts of use in connection with less viscous crude oils. Other methods may be more economical for the recovery of less viscous crudes, as of the date of this application, but this invention may nevertheless find considerable utility in connection with such less viscous crude oils.
The prior art has repeatedly dealt with attempts to find methods for the more efficient recovery of crude oil, including highly acidic crudes.
However, the high viscosity of heavy acidic crudes prevents their economical production with conventional techniques such as simple water flooding. In the past, it has been thought that such crudes can be economically produced only by certain special techniques such as thermal recovery processes. In the copending application of Robert H. Friedman, Ser. No. 312,674, now U.S. Pat. No. 3,874,453, is disclosed a method for recovery of such crudes which includes the injection into an underground formation containing the crude, of a solution of barium hydroxide, Ba(OH).sub.2. In tests with heavy acidic crudes from the San Joaquin Valley (Potter Zone) of California, such crudes having a viscosity of at least about 1000 cp at 75.degree. F and acid numbers in excess of 2.5, it was found that the injection of the barium hydroxide facilitated significant additional recovery of such crudes. In the above-mentioned application, it was pointed out that it is believed that the barium hydroxide injected into the underground formation reacts with the acid in an acidic crude oil to produce a soap which is highly soluble in oil, and preferentially soluble in oil as compared to water. The barium soap thus formed dissolves in the acidic crude, and this soap then acts with the crude to form a grease-like layer at the soap-crude interface. It is believed that this layer acts as a barrier, and thence pushing the crude from behind this layer is effective to move the crude through the formation. Thus, pushing the crude toward a producing well is effective to allow recovery of the crude from the producing well.
This technique is far superior in many contexts of use to simple water flooding. Water flooding often produces fingers of water through the oil and is ineffective to push the greater amount of the crude to a producing well.
Although the barium hydroxide technique is a great improvement over the prior art in many respects, and for many contexts of use, continuing research has revealed that in other contexts of use it still does not yield the percentage oil recovery which would be desired.
The methods provided by this invention, then, comprise part of a continuing effort to provide better and more efficient ways of recovery of more and more crude oil from underground formations, these techniques being directed primarily toward the recovery of highly acidic crudes.